Apparatus and a method for calibration of an industrial robot

ABSTRACT

An apparatus for calibration of an industrial robot, the apparatus comprising a body ( 7 ) having a first angle-measuring member ( 10 ) arranged for measuring an angle relative to the vertical ine about a first measuring axis ( 12 ) and mouting means ( 8, 9, 25 ) for mounting the body to the robot during the calibration. The apparatus comprises a second angle-measuring member ( 11 ) arranged for measuring an angle relative to the vertical line about a second measuring axis ( 13 ) differing from the first measuring axis. A method for calibration of an industrial robot having a plurality of sections movably connected to each for rotation about a plurality of axes, using an apparatus according to claim  1  or  2,  the method comprising: attaching the body ( 7 ) to a section of the robot, reading an angle measurement from the first angle-measuring member ( 10 ), moving the robot about a first axis in dependence of said angle measurement for the first angle-measuring member ( 10 ), reading an angle measurement fro the second angle-measuring member ( 11 ), and moving the robot about a second axis in dependence of said angle measurement from the second angle-measuring member ( 11 ).

This is a continuation of application Ser. No. 09/835,350 filed Apr. 17,2001, now U.S. Pat. No. 6,418,774.

FIELD OF THE INVENTION

The present invention relates to an apparatus for calibration of anindustrial robot, the apparatus comprising a body having a firstangle-measuring member arranged for measuring an angle relative to thevertical line about a first measuring axis and mounting means formounting the body to the robot during the calibration. The presentinvention also relates to a system for robot calibration comprising anindustrial robot and an apparatus for calibration of the industrialrobot. The present invention further relates to a method for calibrationof an industrial robot having a first and a second axis. The presentinvention also relates to a computer program product in connection withthe calibration of an industrial robot.

PRIOR ART

An industrial robot can be viewed as a chain of sections movablyconnected to each other. Two adjacent sections are joined to each otherso that they either are rotatable relative to each other about arotational axis or linearly displaceable relative to each other. Thefirst section in the chain is the base of the robot and the last sectionusually constitutes a tool attachment. For the possibility to determinethe position of the robot, each joint usually is provided with anangle-measuring device in the form of an encoder or a resolverindicating the position of the joint relative to a zero position. Beforean industrial robot can be used it must be calibrated, which means thateach of the angle-measuring devices is calibrated with reference to thezero position. The robot is calibrated in the production plant before itis delivered and sometimes on site before being set to work. Thereafter,the robot is calibrated after larger repairs such as motor or armchanges or after collisions.

In the U.S. Pat. No. 5,239,855, a known method of calibration is shown,in which an inclinometer or some other type of instrument for measuringthe inclination is used to calibrate the angle-measuring devices. Aninclinometer measures the angle between an object and the vertical lineand is, for example, an electronic spirit level. The inclinometer isplaced on a plane of reference on one of the sections, and generates asignal, which is a measure of the angle between the plane of referenceof the section and the vertical line. Thereafter, the joint is moved independence of the generated signal until it has a predetermined anglerelative to the vertical line. The other sections are calibrated in thesame way.

The placement of the planes of reference against which the calibrationdevice is to be attached is predetermined. The planes of referenceconsists of accurately machined surfaces to obtain a high degree offlatness. When the robot is to be calibrated, it is moved to apredetermined calibration configuration. In this configuration, at leastone of the sections is usually oriented in a direction, which differsfrom the directions of the other sections. Usually, the angles betweenthe length axes of the sections are approximately 90°. Thus, the planesof reference may have different directions depending on which section tobe calibrated. The planes of reference are usually either horizontal orvertical during the calibration.

A problem with said method of calibration is that the inclinometer mustbe mounted on the planes of reference of the robot with a very highprecision. The inclinometer is first put on an inclinometer plate, whichis then mounted on an adapter plate. The adapter plate is then attachedto the plane of reference. Depending on the direction of the plane ofreference to be calibrated, today different adapter plates are used.Usually, one type of adapter plate is used for horizontal planes ofreference and another type of adapter plate is used for vertical planes.This way of attaching the inclinometer to the robot includes a largenumber of sources of error. Examples of sources of error are mountingerrors between the adapter plate and the plane of reference of therobot, mounting errors between the inclinometer plate and the adapterplate, and errors of tolerance of the adapter plate. The fact thatseveral different adapter plates are used also contributes to increasingthe mounting error.

An apparatus for calibration of an articulated robot is shown in U.S.Pat. No. 4,505,049. The calibration apparatus comprises an inclinometerprovided on an inclinometer plate, which is mounted on one sidepiece ofan L-shaped adapter plate. The other sidepiece of the L-shaped adapterplate has a flat surface adapted for being in contact with the plane ofreference during the calibration. The flat surface of the adapter plateis provided with positioning means projecting from the surface and isadapted to fit in with corresponding receiving means formed in the planeof reference. The object of the positioning means is to establish adefinitely determined positional relation between the surface and theplane of reference.

A common type of industrial robot comprises a base adapted for restingon a horizontal foundation and a stand, which is rotationally arrangedrelative to the base about a first vertical axis. Since the first axisis essentially parallel with the vertical line, it cannot be calibratedwith an inclinometer attached to the stand. Accordingly, a secondproblem with the method of calibration described above is that it cannotcalibrate rotational axes parallel with the vertical line.

SUMMARY OF THE INVENTION

The present invention has been developed to obviate the above-describeddisadvantages of the prior art and has as its object the provision of anapparatus and a method and a computer program product for calibration ofan industrial robot, wherein the error during the mounting of the bodyon the plane of reference is reduced.

The apparatus according to the present invention is characterised inthat the apparatus comprises a second angle-measuring member arrangedfor measuring an angle relative to the vertical line about a secondmeasuring axis differing from the first measuring axis. By having twoangle-measuring members arranged with an angle relative to each other,it is possible to calibrate in two directions without having to rotatethe angle-measuring member. Advantageously, the second angle-measuringmember is arranged essentially perpendicularly to the firstangle-measuring member. This means that two axes being perpendicular toeach other can be calibrated without reorientation of the body. This isadvantageous, for example when the wrist axes are to be calibrated, i.e.the axes 3, 4, 5, and 6, for a robot having six axes. When the robot isin its predetermined calibration configuration, the axes 4 and 6 areparallel to each other and the axes 3 and 5 are perpendicular to theaxes 4 and 6. During the calibration of the wrist axes, the body isplaced on the outermost section, which is usually a tool attachment.Thanks to the fact that the body comprises two angle-measuring membersarranged perpendicularly to each other, all four axes can be calibratedwithout moving the body.

According to an embodiment of the invention, the mounting arrangementcomprises three protruding contact elements being arranged so that thebody is in contact with the plane of reference through said contactelements during the calibration. The calibration apparatus and the robotare connected to each other through the contact elements. By using threecontact elements the contact area between the calibration apparatus andthe plane of reference is reduced without reducing the stability in theconnection. By reducing the contact area between the calibrationapparatus and the robot, the mounting error is reduced as well. Withthree contact elements, there are at least three contact points betweenthe body and the plane of reference of the robot, which means that theangle-measuring member and the robot are fixed relative to each otherwith at least three degrees of freedom. A stable attachment of the bodyagainst the robot is thus obtained. By positioning the contact elementsso that they form corners of a triangle maximum stability is achieved.

According to an embodiment of the invention, each of the contactelements comprises a flat portion adapted for being in contact with theplane of reference during the calibration. From a manufacturing point ofview it is an advantage to make the portion adapted for being in contactwith the plane of reference flat.

According to a further embodiment of the invention, the mountingarrangement further comprises an attachment element for attaching thebody to the plane of reference. Preferably, the attachment element is ascrew. Thereby, a reliable and inexpensive attachment is obtained.Further, the screw and a corresponding hole in the plane of referencefacilitates the positioning of the body relative to the plane ofreference.

According to a further embodiment of the invention, the apparatusfurther comprises a mounting member for pivotally connecting the body tothe robot. By this arrangement, it is possible to calibrate anessentially vertical axis of the robot by mounting the body to the robotsuch that the body, including the angle-measuring member, forms apendulum. Hence, it will be possible to calibrate all the axes of therobot using one single body. In a further embodiment, the mountingmember comprises a shaft having with an attachment element for attachingthe shaft to the robot, the body being arranged pivotal about thatshaft.

According to a further embodiment of the invention, the apparatuscomprises a calibration element for mounting to the robot and the bodycomprises a portion adapted for being in contact with said calibrationelement during calibration. The robot comprises a first and a secondsection, the second section being coupled to the first section forrotation about an essentially vertical axis through the first section.For calibration of the vertical axis through the first section, the bodyis mounted to the second section and the calibration element is mountedto the first section. The robot is moved until the portion of the bodyis in contact with the calibration element mounted on the first section.When the second section is moved further, the calibration element pushesthe body so that it pivots about the shaft, thus causing an angularchange of the angle-measuring member. Since the signal from theangle-measuring member depends on the relative position between thefirst and the second section, it is possible to calibrate the verticalaxis through the first section.

According to a further embodiment of the invention, the body is shapedso that its centre of gravity is displaced in relation to an axisthrough said mounting member and said portion adapted for being incontact with said calibration element. Thanks to the fact that thecentre of gravity is displaced in relation to that axis, the measuringaxis deviates from the vertical line when the body is moved into contactwith the calibration element and thus it is possible to measure on bothsides of the vertical line. The size of the displacement determines thesize of the angular interval possible to measure before the measuringaxis coincides with the vertical line.

According to a further embodiment of the invention, the body isessentially L-shaped having a first and a second branch arrangedessentially perpendicularly to each other, said mounting member and saidportion being located at or in the vicinity of the first branch. Such abody has a centre of gravity, which is displaced in relation to an axisthrough said mounting member and said portion adapted for being incontact with said calibration element when said mounting member ismounted to the stand of the robot.

According to a further embodiment of the invention, the body comprises asecond mounting arrangement for mounting the body to a second plane ofreference on the robot, said second mounting arrangement being arrangedin an angle relative to the first mounting arrangement, said angleessentially corresponding to the angle between two planes of referenceof the robot when the robot is in its calibration configuration. Withsuch a second mounting arrangement, the same body can be used forcalibration of planes of reference being arranged in two differentdirections. Accordingly, there is no need for using differentcalibration bodies or different adapter plates, such as in the priorart, for measuring two planes of reference with different anglesrelative to the vertical line. The consequence of this is that a sourceof error, which is difficult to master during calibration, directlydisappears. The second mounting arrangement is preferably arrangedessentially perpendicularly to the first mounting arrangement. If themounting arrangements are arranged perpendicularly against each other,both horizontal and vertical planes of reference can be measured withthe same body.

According to a further embodiment of the invention, the first mountingarrangement comprises key means adapted for cooperation withcorresponding key means on the first plane of references, and the secondmounting arrangement comprises key means adapted for cooperation withcorresponding key means on the second plane of reference, the key meansof the first mounting arrangement differing from the key means of thesecond mounting arrangement. The key means ensures that an operatorattaches the body to the right calibration plane and in a rightposition. Thus, the key-means prevents the operator from by mistakemounting the body to the plane of reference in a wrong way. Since thebody is provided with two mounting arrangements, there are twopossibilities to mount the body on the plane of reference, but only oneis correct. The key means of a certain plane of reference only fits inwith the correct mounting arrangement and thus misplacement is avoided.

According to a further embodiment of the invention, each key means ofthe mounting arrangements comprises at least two protruding elementsadapted to fit in with corresponding notches in the plane of referenceand that the distance between the protruding elements differs betweenthe first mounting arrangement and the second mounting arrangement.

According to a further embodiment of the invention, each key means ofthe mounting arrangements comprises at least one protruding elementadapted to fit in with a corresponding notch in the plane of reference,and the key-means have different shape, such as wedge-shaped orquadrangular. The protruding elements can for instance differ by havingdifferent diameters or height.

According to a further embodiment of the invention, each key means ofthe mounting arrangements comprises at least one protruding elementadapted to fit in with a corresponding notch in the plane of reference,and the key-means of the first and the second mounting arrangement havedifferent shape. Preferably, the protruding element has an asymmetricalshape so that it only fits in one position relative to the correspondingnotch.

According to a further embodiment of the invention, the robot isconnected to a control system via a cabling member adapted fortransferring power and signals between the robot and the control systemand the apparatus comprises a junction member electrically connected tothe angle-measuring member, the junction member being provided with aconnector for connection to said cabling member and means fortransferring power to the angle-measuring member and transferringmeasurement values from the angle-measuring member via said cablingmember. By such an arrangement, the cable member being used fortransferring power and signals between the robot and the control systemcan also be used for transferring power and signals between the controlsystem and the angle-measuring member. An advantage with thisarrangement is that the robot does not have to be provided with anyextra cable for the calibration. By providing the calibration apparatuswith such a junction member, the expenses in connection with providingeach robot with an extra cable is avoided.

The method according to the present invention comprises: attaching thebody to a section of the robot, reading an angle measurement from thefirst angle-measuring member, moving the robot about a first axis independence of said angle measurement from the first angle-measuringmember, reading an angle measurement from the second angle-measuringmember, and moving the robot about a second axis in dependence of saidangle measurement from the second angle-measuring member.

According to an embodiment of the invention, the method furthercomprises: attaching the body to a section of the robot, reading anangle measurement from the first angle-measuring member, moving therobot about a first axis in dependence of said angle measurement fromthe first angle-measuring member, reading an angle measurement from thesecond angle-measuring member, and moving the robot about a second axisin dependence of said angle measurement from the second angle-measuringmember.

The computer program product according to the invention comprises acomputer-readable medium, having thereon a computer readable programmeans which, when run on a computer, makes the computer performcalibration of an industrial robot with the calibration apparatusaccording to the invention, including receiving an angle measurementfrom the first angle-measuring member, sending control signals to therobot about moving a first axis of the robot in dependence of said anglemeasurement from the first angle-measuring member, receiving an anglemeasurement from the second angle-measuring member, and sending controlsignals to the robot about moving a second axis in dependence of saidangle measurement from the second angle-measuring member. Thus, thecalibration is made automatically and therefore becomes more precise andaccurate.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be explained by different embodimentsdescribed as examples with reference to the appended drawings.

FIG. 1 shows an industrial robot in a calibration configuration having acalibration apparatus according to the invention mounted thereupon.

FIG. 2 is in a perspective view showing an embodiment of a calibrationapparatus according to the invention.

FIG. 3 is a perspective view showing how the angle-measuring members arepositioned relative to each other in the calibration apparatus.

FIG. 4 a is a side view showing a first side of the calibrationapparatus in FIG. 2.

FIG. 4 b is a side view showing a second side of the calibrationapparatus in FIG. 2.

FIG. 5 is a sectional view showing the calibration apparatus and theplan of reference of the robot during calibration.

FIGS. 6 a–6 c are perspective views showing the body and the robotduring calibration of an essentially vertical axis.

FIG. 7 shows the electrical connection of the calibration apparatusaccording to an embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

FIG. 1 shows an example of an industrial robot standing in a calibrationconfiguration. The robot comprises a base 1, which is firmly mounted ona foundation. The robot further comprises a stand 2, which is rotatablerelative to the base 1 around a first vertical axis. In the top end ofthe stand 2, a first robot arm 3, is rotatably mounted about a secondhorizontal axis. In the outer end of the first arm 3, a second arm 4 isrotatably mounted relative to the first arm about a third axis. Thesecond robot arm 4 comprises two parts, 4 a and 4 b, and the outer part4 b being rotatable relative to the inner part 4 a around a fourth axiscoinciding with the longitudinal axis of the second arm 4. In its outerend, the second arm 4 supports a so-called robot hand 5, which isrotatable about a fifth axis, which is perpendicular to the length axisof the second arm 4. The robot also comprises a tool attachment 6. Theouter part of the robot hand with the tool attachment 6, is rotatablerelative to the inner part of the robot hand about a sixth axis. Foreach of the axes of the robot, there is a level indicator giving asignal, which is a measure of the present rotational angle of the axis.The output signal from the level indicator is transmitted to a controlsystem of the robot.

When the robot is in its calibration configuration, the axis of therobot are in their calibration position, as shown in FIG. 1, the firstarm 3 is placed parallel with the first axis, i.e. parallel with thevertical line, the second arm 4 is placed perpendicular to the first arm3 and the robot hand 5 is placed parallel with the length axis of thesecond arm, i.e. perpendicular to the vertical line. On an industrialrobot, there is usually a plurality of especially formed planes ofreference intended for being used during calibration of the robot. InFIG. 1, a body 7 according to the invention is shown arranged on some ofthese planes of reference. A first plane of reference on the robot isarranged on the base 1, a second plane of reference is arranged on thefirst arm 3, a third plane of reference is arranged on the second arm 4,and a fourth and last plane of reference is arranged on the toolattachment 6. The fourth plane of reference may also be provided on adetachable plate attached to the tool during the calibration.

FIGS. 2 show an embodiment of a calibration apparatus according to theinvention. The apparatus comprises a body 7 having a first and a secondmounting arrangement 8, 9 for mounting the body to the planes ofreference of the robot. The body further comprises two angle-measuringmembers 10, 11 in the form of inclinometers measuring the angle of anobject relative to the vertical line. An inclinometer functions as anelectronic level and measures the inclination angle about a measuringaxis. The inclinometers 10, 11 are positioned with their measuring axes12, 13 perpendicular to each other. FIG. 3 shows the angle-measuringmembers 10, 11 in more detail.

The body 7 is essentially L-shaped having a first and a second branch 7a, 7 b arranged essentially perpendicularly to each other. The firstmounting arrangement 8 is mounted on a surface of the first branch 7 aand the second mounting arrangement 9 is mounted on a surface of thesecond branch 7 b. Accordingly, the mounting arrangements are arrangedperpendicularly to each other. The first angle-measuring member 10 ispositioned with its measuring axis 12 essentially parallel to thesurface of the first branch 7 a and perpendicularly to the surfacesecond branch 7 b. The second angle-measuring member 11 is positionedwith its measuring axis 13 essentially perpendicularly to the surface ofthe first branch 7 a and parallel to the surface second branch 7 b.

FIG. 4 a shows a front view of the surface of the first branch 7 a. Thefirst mounting arrangement 8 comprises three protruding contact elements15 adapted for being in contact with the plane of reference during thecalibration, an attachment element 17 for removably attaching the bodyto the plane of reference and key means 19 adapted for fitting in withcorresponding key means on the plane of references. The contact elements15 are arranged so that the body 7 is in contact with the plane ofreference through the contact elements during the calibration. In thisembodiment, the contact elements 15 are cylindrical and one end thereoffixedly connected to the surface of the body and the other end flat andintended to bear on the surfaces of the plane of reference or on a platehaving a corresponding function, which plate is mounted on the robot.The three contact elements 15 are arranged as the corners of a triangle.

In a preferred embodiment, the attachment element 17 is a screw intendedto be attached to a corresponding hole with threads provided in theplane of reference. Alternatively, a magnet, a spring arrangement or abayonet may be used as an attachment element. The key means 19 comprisestwo protruding elements adapted to fit in with corresponding notches inthe plane of reference. The distance d₁ between the protruding elementsis the same as the distance between the corresponding notches in theplane of reference. The body shall be differently orientated dependingon which of the calibration plans the body shall be mounted to. The keymeans helps the robot operator to position the body correctly to theplane of reference.

FIG. 4 b shows a front view of the surface of the second branch 7 b. Thesecond mounting arrangement 9 comprises three protruding contactelements 20, an attachment element 21, and key means 22 arranged in thesame manner as in the first mounting arrangement 8. The distance d₂between the protruding elements 22 of the second mounting arrangement 9differs from the distance d₁ between the protruding elements 19 of thefirst mounting arrangement 8. Hence, it is impossible to mount themounting arrangement to the wrong plane of reference and accordingly thebody will always be correctly orientated. The first mounting arrangement8 fits in with the first and the third plane of reference and the secondmounting arrangement 9 fits in with the second and the fourth plane ofreference. For small robots, it is possible to reduce the number ofplanes of reference to only three. The third, fourth, fifth, and sixthaxis can be calibrated using the same plane of reference, e.g. the planeof reference of the tool attachment 6.

FIG. 5 shows how the first branch 7 a of the body is mounted to a planeof reference 23 of the robot. The contact elements 15 are bearing on theflat surface of the plane of reference, the screw 17 is engaged to acorresponding hole in the plane of reference, and the protrudingelements 19 of the key means are recessed in corresponding notches 24 inthe plane of reference 23.

During the calibration process, the body 7 is attached through the firstmounting arrangement to the plane of reference on the base 1 of therobot. Reference angles are read from the first and the secondangle-measuring member. The reference angles are stored in the controlsystem of the robot. Thereafter, the axes 26 are calibrated byattachment of the body 7 to the other planes of reference, reading anyof the inclinometers and calculating the difference between the readangle and the angle of reference of that inclinometer. This calculationis performed in the control system of the robot. Thereafter, the controlsystem orders the axis being calibrated to move in dependence of thecalculated difference until the difference has a predetermined value andthe axis ends up in its calibration position. Usually, the predeterminedvalue of the difference is zero. During calibration of the wrist axes,i.e. the axes 5 and 6, the body 7 is attached by the second mountingarrangement to the tool attachment 6. Thus, the same body can be used tocalibrate axes, which are perpendicular to each other.

The axes 2–6 of the robot are possible to calibrate with the bodyattached to the planes of reference. But the first axis of the robot,which axis is parallel to the vertical line, is not possible tocalibrate in the same manner. For calibration of the first axes of therobot, the calibration apparatus is provided with a mounting member 25for pivotal connection of the body 7 to the stand 2 of the robot. Themounting member 25 comprises a shaft 27, an attachment element forattaching the shaft 27 to the stand 2. The attachment element comprisesa tapering part 28 and a screw 29 adapted to fit in with a correspondinghole in the stand 2. The body is arranged pivotally about the shaft 27.

The shaft 27 is located in a through-hole in the first branch 7 a of thebody 7. The axis 30 of the shaft 27 is arranged perpendicular to themeasuring axis 12 of the first angle-measuring member 10. Thecalibration apparatus further comprises a calibration element formounting to the base 1 of the robot and the body comprises an elongatedprotruding portion 32 adapted for being in contact with said calibrationelement during calibration of the first axis. The portion 32 is locatedin the outer corner connecting the first and the second branch of thebody. The longitudinal axis of the portion 32 is parallel to the axis 30of the shaft 27. In another embodiment, the portion 32 consists of a rodpositioned in a recess in the body 7.

FIG. 6 a shows the calibration apparatus when it is used for calibrationof the first axis of the robot. The body 7 is pivotally attached to thestand 2 of the robot through the shaft 27. An elongated calibrationelement 35 is mounted to the base 1 of the robot. The calibrationelement 35 is vertically positioned on the base. The calibration element35 is arranged such that it is removable from the base after thecalibration has been carried out. Due to the L-shape of the body, thecentre of gravity of the body is displaced in relation to an axisthrough the mounting member 27 and the portion 32. The displacement isabout 5 mm. Therefore, the surface of the first branch 7 a is notvertical when the body is connected to the stand 2 and consequently themeasuring axis 13 of the second inclinometer 11 is not vertical. Thus,the measuring angle differs from the vertical line.

The calibration of the first axes is illustrated in FIGS. 6 a–6 c. Tobegin with, the calibration element 35 is mounted to the base 2 and thebody is attached to the stand 2 by attaching the mounting member 25 tothe stand 2. The stand 2 is then moved to a rough calibration position,i.e. a position close to the calibration position. A rough calibrationposition is within 10° from the actual calibration position. At widerangles, the inclinometers may not work properly. The angle measurementsfrom the first inclinometer 10 are read during the calibration. Theangle measurements correspond to the angle between the measuring axis 12and the vertical line. Thereafter, the stand 2 is moved about the firstaxis until the body is in contact with the calibration element 32 andthe stand 2 is further moved in response to said measured angle untilthe first axis is calibrated, i.e. the axis ends up in its calibrationposition. As shown in the FIGS. 6 a–6 c the body 6 functions as apendulum rotating about a horizontal axis during the calibration of thefirst axis.

In an embodiment of the invention, the calibration is controlled bysoftware in the control system of the robot. The control system receivessignals from any of the inclinometers, which signals correspond to theangle between the measuring axis of the inclinometer and the verticalline. The software produces control signals in response to the receivedsignals from the inclinometer and then sends the control signals to therobot. The robot is moved in accordance with the received controlsignals until the axis is in its calibration position. This method isrepeated for each axis until all the axes of the robot are calibrated.The control system comprises necessary equipment, such as a processor,memory, and I/O units, for running the software, which performs thecalibration.

FIG. 7 shows a robot 40 connected to a control unit 42 comprising thecontrol system of the robot. The control unit 42 is coupled to the robotvia a cabling member 44 adapted for transmitting signals and databetween the robot 40 and the control unit 42 and for transmitting powerto the robot. The calibration apparatus according to an embodiment ofthe invention comprises a junction member 46 electrically connected tothe angle-measuring members 10, 11 of the body 7 via two cables 47, 48.The junction member 46 comprises a first connector 49 for connection ofthe cabling member 44 to the control unit 42, a second connector 50 forconnection of a second cabling member 51 to the robot 40 and aseries-measuring card adapted for transmitting power to theangle-measuring member and transmitting measurement values from theangle-measuring members via the cabling member 44 to the control system.

During normal operation of the robot, the control unit 42 is connectedto the robot 40 via the cabling member 44, which is connected to therobot. During calibration of the robot, the control unit 42 is connectedto the robot 40 via the cabling member 44, the junction member 46 andthe cabling member 51. The angle-measuring members of the body 7 aresupplied with power and signals are transmitted to the control unit viathe cabling member 44, the junction member 46 and the cables 47 and 48.

The present invention is not limited to the embodiments disclosed butmay be varied and modified within the scope of the following claims. Therobot may in some applications be mounted at the ceiling, with the baselocated above the stand. The calibration apparatus of the presentinvention can be used for calibration of the first axis when the robotis mounded upside down, if the body and the calibration element areattached to each other by any resilient means, such as a rubber band,for avoiding that the body rotates due to the gravity.

The body may have different shapes, but should preferable comprise twoflat plan, for example the body can be cubical.

It is also possible to provide the base with more than one calibrationelement. If it is difficult to reach the calibration element during thecalibration it is advantageous to have a plurality of calibrationelement to chose between. The calibration element may either beremovable or fixtly mounted. The calibration element may consist of amachined portion of the base.

In another embodiment, the body is used as a pendulum for calibration ofthe non-vertical axes as well as the vertical axes of the robot. In thisembodiment the calibration element and the body is mounted on the samesection during calibration. This embodiment is advantageous since it issufficient to provide the body with one mounting means, the pivotalmounting member.

The order in which the axes are calibrated could of course be differentfrom the order described above, for example the first axis may becalibrated before the other axes.

The present invention is also useful for parallel cinematicmanipulators.

1. An apparatus for calibration of an industrial robot, the apparatuscomprising a body having a first angle-measuring member arranged formeasuring an angle relative to the vertical line about a first measuringaxis, mounting means for mounting the body to the robot during thecalibration, and a second angle-measuring member arranged for measuringan angle relative to the vertical line about a second measuring axisdiffering from the first measuring axis, wherein said mounting meanscomprises a first mounting arrangement for mounting the body to a planeof reference of the robot, the mounting arrangement comprising threeprotruding contact elements being arranged so that the body is incontact with the plane of reference through said contact elements duringthe calibration, wherein said mounting means further comprises a secondmounting arrangement for mounting the body to a second plane ofreference on the robot, wherein said second mounting arrangement isarranged in an angle relative to the first mounting arrangement, andwherein said angle essentially corresponds to the angle between twoplanes of reference of the robot when the robot is in its calibrationconfiguration.
 2. The apparatus according to claim 1, wherein the secondangle-measuring member is arranged with its measuring axis essentiallyperpendicular to the measuring axis of the first angle-measuring member.3. The apparatus according to claim 1, wherein each of the contactelements comprises a flat portion adapted for being in contact with theplane of reference during the calibration.
 4. The apparatus according toclaim 1, wherein the contact elements are arranged so that they formcorners of a triangle.
 5. The apparatus according to claim 1, whereinthe first mounting arrangement comprises an attachment element forattaching the body to the plane of reference.
 6. The apparatus accordingto claim 5, wherein the attachment element is a screw.
 7. The apparatusaccording to claim 1, wherein the first mounting arrangement is arrangedin a first plan and the second mounting arrangement is arranged in asecond plane being essentially perpendicular to the first plan.
 8. Theapparatus according to claim 1, wherein the first mounting arrangementcomprises key means adapted for cooperating with corresponding key meanson the first plane of references, that the second mounting arrangementcomprises key means adapted for cooperating with corresponding key meanson the second plane of reference, and that the key means of the firstmounting arrangement differs from the key means of the second mountingarrangement.
 9. The apparatus according to claim 8, wherein each keymeans of the mounting arrangements comprises at least one protrudingelement adapted to fit in with a corresponding notch in the plane ofreference, and the key-means of the first and the second mountingarrangement have different shape.
 10. The apparatus according to claim8, wherein each key means of the mounting arrangements comprises atleast two protruding elements adapted to fit with corresponding notchesin the plane of reference and that the distance between the protrudingelements differs between the first mounting arrangement and the secondmounting arrangement.
 11. The apparatus according to claim 1, whereinthe mounting means further comprises a mounting member for pivotallyconnecting the body to the robot.
 12. The apparatus according to claim11, wherein said mounting member comprises a shaft having an attachmentelement for attaching the shaft to the robot, the body being arrangedpivotal about that shaft.
 13. The apparatus according to claim 11,further comprising: a calibration element for mounting to the robot,wherein the body comprises a portion adapted for being in contact withsaid calibration element during calibration.
 14. The apparatus accordingto claim 13, wherein the body is shaped so that its center of gravity isdisplaced in relation to an axis through said mounting member and saidportion adapted for being in contact with said calibration element. 15.The apparatus according to claim 13, wherein the body is essentiallyL-shaped having a first and a second branch essentially perpendicular toeach other, said mounting member and said portion being located at or inthe vicinity of the first branch.
 16. The apparatus according to claim1, wherein the robot is connected to a control system via a cablingmember adapted for transferring power and signals between the robot andthe control system, wherein the apparatus further comprises a junctionmember electrically connected to the angle-measuring member, thejunction member being provided with a connector for connection to saidcabling member and means for transferring power to the angle-measuringmember and transferring measurement values from the firstangle-measuring member and second angle-measuring member via saidcabling member.
 17. A method for calibration of an industrial robothaving a plurality of sections movably connected to each for rotationabout a plurality of axes, using an apparatus according to claim 1, themethod comprising: attaching the body to a section of the robot, readingan angle measurement from the first angle-measuring member, moving therobot about a first axis in dependence of said angle measurement fromthe first angle-measuring member, reading an angle measurement from thesecond angle-measuring member, and moving the robot about a second axisin dependence of said angle measurement from the second angle-measuringmember.
 18. The method for calibration of an industrial robot accordingto claim 17, comprising: providing the robot with a protrudingcalibration element, pivotally attaching the body to a section beingmovable about an essentially vertical axis, moving the section aboutsaid vertical axis until the body is in contact with the calibrationelement, reading an angle measurement from the first angle-measuringmember, and moving the section about said vertical axis in dependence ofsaid angle measurement from the first angle-measuring member.
 19. Themethod for calibration of an industrial robot according to claim 17,wherein the step of attaching the body to a section of the robotcomprises: bringing the contact elements of the calibration body intocontact with a plane of reference on the robot, and attaching thecalibration body to the plane of reference.
 20. A computer programproduct comprising a computer readable medium, having thereon a computerreadable program means which, when run on a computer, makes the computerperform calibration of an industrial robot with a calibration apparatusaccording to claim 1, the computer program means comprising computerprogram instructions executable by a process for performing the stepsof: receiving an angle measurement from the first angle-measuringmember, sending control signals to the robot about moving a first axisof the robot in dependence of said angle measurement from the firstangle-measuring member, receiving an angle measurement from the secondangle-measuring member, and sending control signals to the robot aboutmoving a second axis in dependence of said angle measurement from thesecond angle-measuring member.